Investments in Debt and Equity Securities (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Schedule of Investments in Debt and Equity Securities
Cost Basis	$ 1,294	$ 1,317
Unrealized Pretax Net Gains (Losses)	68	50
Fair Value	1,362	1,367
U.S. treasury bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	9	9
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	9	9
Other U.S. and non-U.S. government bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	58	60
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	58	60
Corporate bonds
Schedule of Investments in Debt and Equity Securities
Cost Basis	479	489
Unrealized Pretax Net Gains (Losses)	3	3
Fair Value	482	492
Asset-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	88	90
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	88	90
U.S. governmental agency mortgage-backed securities
Schedule of Investments in Debt and Equity Securities
Cost Basis	214	225
Unrealized Pretax Net Gains (Losses)	(2)	(2)
Fair Value	212	223
Residential
Schedule of Investments in Debt and Equity Securities
Cost Basis	9	10
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	9	10
Commercial
Schedule of Investments in Debt and Equity Securities
Cost Basis	31	36
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	31	36
Large capitalization value
Schedule of Investments in Debt and Equity Securities
Cost Basis	281	280
Unrealized Pretax Net Gains (Losses)	44	32
Fair Value	325	312
Real estate investment trust (REIT)
Schedule of Investments in Debt and Equity Securities
Cost Basis	84	77
Unrealized Pretax Net Gains (Losses)	4	2
Fair Value	88	79
Smaller company growth
Schedule of Investments in Debt and Equity Securities
Cost Basis	41	41
Unrealized Pretax Net Gains (Losses)	19	15
Fair Value	$ 60	$ 56